If I come across a credit card in the trash, and use it, am I not guilty of theft? If I find the key to your house, and go in and help myself to a meal, is that not a crime? If the waitress overhears that you are going on vacation and forgot to lock the door (wife tell husband in restaurant “I thought you locked up! Oh well, it’s a safe neighnorhood, why go back) – is she not liable if she accepts your invitation to use her house.
In fact, virtually all “Insider trading” cases involve directors, employees, or their agents – not homeless people and waitresses (even ignoring that very few homeless people can raise the money to buy securities).